Recently, television screens are becoming larger and their resolutions are becoming higher. At the same time, televisions are rapidly becoming thinner. Conventionally, televisions have been mounted on television cabinets or on television stands; however, recent televisions are thinner, and thus can be wall-mounted. It is expected that televisions will become even thinner and more users will mount their televisions on their walls.
Wall-mounting a television has an advantage of making effective use of a room space. Meanwhile, in an adjacent room across a wall on which the television is mounted, a speaker built in the television set, which is a sound source, is close to the wall when compared to a conventional installation method. This results in louder sound leakage from the built-in speaker to the adjacent room.
As an example of the sound transmission loss characteristic of a general residential wall, FIG. 28 shows the sound transmission loss characteristic of a double-layer plasterboard (12 cm thick) that is widely used for an internal wall of collective housing. In FIG. 28, at high frequency, a sound transmission loss is larger, which results in less sound leakage, while at low frequency, a sound transmission loss is less, which results in more sound leakage. Accordingly, a solution to decrease the sound leakage to the adjacent room, especially at low frequency, is necessary.
When a television is made thinner, a built-in speaker also needs to be made smaller and thinner. However, the smaller and thinner speaker cannot output a low-frequency sound at a sufficient level. For this reason, it is difficult for a recent wall-mounted television to provide a dynamic sound despite its large screen and high-definition images. This causes the viewer to feel uncomfortable. Accordingly, in the space where the viewer is located, a solution to increase the sound pressure level at low frequency is necessary.
As televisions are improved, especially made thinner, two opposite needs have risen. One is that, in the space where the viewer is located, the sound pressure level at low frequency needs to be increased, and the other is that, in the space of the room adjacent to the space where the viewer is located, the sound pressure level at low frequency needs to be decreased. For example, Patent Document 1 discloses a configuration of a conventional technique that realizes a desired acoustic output characteristic in a predetermined region and cancels a sound in a different predetermined region.
FIG. 29 is a block diagram illustrating a configuration of a loud speaker device disclosed in Patent Document 1. A conventional loud speaker device includes first signal processing means 1a, second signal processing means 1b, a delay device 2, a first sound source 3a, a second sound source 3b, a first detector 4a, a second detector 4b, and an adder 5. The first signal processing means 1a receives an acoustic signal. The second signal processing means 1b receives the signal processed by the first signal processing means 1a. The delay device 2 receives the acoustic signal and performs a given delay control on the acoustic signal and outputs a resultant signal. The first sound source 3a outputs a sound generated from the signal processed by the first signal processing means 1a. The second sound source 3b outputs a sound generated from the signal processed by the second signal processing means 1b. It is assumed that the first sound source 3a and the second sound source 3b are ideal speakers that output only sounds converted based on the signals processed by the first signal processing means 1 and by the second signal processing means 1b, respectively. The first detector 4a is arranged close to the first sound source 3a and detects the radiated sound from the first sound source 3a. The second detector 4b is arranged close to the second sound source 3b and detects the radiated sound from the second sound source 3b. The adder 5 adds the output from the delay device 2 to the output from the first detector 4a, and inputs the result to the first signal processing means 1a. Next, an operation of the loud speaker device in FIG. 29 will be described.
A delay amount is set to the delay device 2, the delay amount being about the same amount of time taken from the time when an acoustic signal is inputted to the first signal processing means 1a to the time when the sound is detected by the first detector 4a. The first signal processing means 1a controls the acoustic signal so that the output from the adder 5 becomes smaller, and outputs the resultant signal to the first sound source 3a and the second signal processing means 1b. The second signal processing means 1b controls the output from the first signal processing means 1a so that the output from the second detector 4b becomes smaller, and outputs the result to the second sound source 3b. 
In accordance with the operation described above, the sum of the output from the first detector 4a and the output from the delay device 2 becomes closer to 0. In short, at the position of the first detector 4a, the pressure of a sound, whose acoustic signal is delayed for a predetermined time, can be obtained, the phase of the acoustic signal being inverted. Accordingly, if given a signal in opposite phase to a desired acoustic signal, the first sound source 3a can radiate a sound having a desired acoustic characteristic, at the position of the first detector 4a. 
Meanwhile, the output from the second detector 4b becomes closer to 0. In short, at the position of the second detector 4b, the radiated sound from the first sound source 3a is cancelled by the sound radiated from the second sound source 3b. 
Accordingly, the loud speaker device having the configuration shown in FIG. 29 can impart a desired acoustic characteristic to the radiated sound detected by the first detector 4a, and simultaneously reduce the radiated sound detected by the second detector 4b. 